This invention relates to removal of an amine borane complex from plating solutions. An amine borane containing plating solution is adsorbed onto a solid support. The solid support is then treated with an oxidizing agent which oxidizes the amine borane without generating hydrogen gas. The oxidized amine borane can be collected for environmentally benign disposal.
Electroless plating is a process which allows for the reduction of metal ions in solution and subsequent deposition of metal onto a substrate without the use of electrical energy. The driving force for the reduction of metal ions and their deposition is supplied by a chemical reducing agent in solution, such as an amine borane. Amine boranes are generally prepared by reacting primary, secondary or tertiary amine with diborane in stoichiometric amounts. A number of amine borane complexes useful for metal plating are described in U.S. Pat. No. 3,295,999 and U.S. Pat. No. 3,338,726 both of which are incorporated by reference herein.
Amine borane reducing agents dissociate in neutral, near neutral or acidic pH environments generating copious amounts of hydrogen. For example every mole of dimethylamine borane (DMAB) that dissociates generates approximately 3 moles of hydrogen gas. Typically, when DMAB is used in an electroless plating solution, dissociation is avoided since the electroless chemical deposition solution is always maintained at a highly alkaline pH. However, rinsing with deionized water which is at neutral pH after the deposition step creates conditions conducive to breakdown of a reducing agent such as DMAB. If the rinse station is remotely located from the waste treatment station this can result in hydrogen gas accumulation on the piping to the waste station, a dangerous situation. Such remote location of the rinsing station from the waste station is commonly found in the semiconductor industry where electroless cobalt solutions include amine boranes, for example dialkylamine boranes such as DMAB or diethylamine borane as reducing agents. Typically, the deposition and rinse stations are part of an automated tool located in the fabrication area or clean room. In contrast, waste treatment equipment is typically located outside the fabrication area or clean room remote from the rinsing station.
Unfortunately, while amine borane complexes are useful as reducing agents in electroless plating processes, the disposal of these materials is a significant environmental concern. For example, boron is toxic to plants in excess of a fraction of parts per million (ppm). Therefore, the presence of boron is typically restricted in industrial effluents in areas where municipalities recycle wastewater for irrigation. Accordingly, there is a need for a process that provides for the environmentally benign disposal of amine borane complexes used in industrial processes.
It is an object of the invention to provide a process for the environmentally benign disposal of amine borane complexes used in plating.
Another object of the invention is to provide a method of separating amine borane complex from plating solutions at a location at or proximate to a rinsing station.
A further object of the invention is to provide a method of reducing the amount of amine borane complex in plating solutions which avoids hydrogen generation.
These and other objects of the invention are achieved by conveying a plating solution including an amine borane complex through an adsorbent bed, adsorbing the amine borane complex on the adsorbent bed, conveying a second solution comprising an oxidizing agent through the adsorbent bed wherein the amine borane complex is oxidized and forms decomposition products and eluting a liquid including the decomposition products from the adsorbent bed, and collecting the eluted amine borane decomposition products.